Method for finishing paper and paper products

ABSTRACT

Process for finishing paper and paper products by treating the surface of paper or paper products with at least one finishing agent, at least one finishing agent being applied in the form of a pattern on the top and/or bottom of paper or paper products, and the papers and paper products obtainable by the process.

The invention relates to a process for finishing paper and paper products by treating the surface of paper and paper products with at least one finishing agent, and the finished paper and paper products obtainable by the process.

In order to improve the properties of paper and paper products, for example, the surface of paper or paper products is treated with finishing agents, such as strength agents, water repellants, hydrophilizing agents and/or paper coating slips. The finishing agents are always applied over the whole area on the top and/or the bottom of the paper or of the paper products.

The prior German Application 10 2005 050 658.5 discloses a process for reducing the absorption of water and water vapor and for increasing the dimensional stability of paper and paper products. There, cellulose fibers or a paper product obtained therefrom by draining on a wire are or is first compressed, the compressed paper product is then brought into contact with an aqueous solution and/or dispersion of the reactive material, the compression is then eliminated with further action of the aqueous solution and/or dispersion and the paper product is dried and is heated to a temperature at which the reactive material reacts with itself and/or with the cellulose fibers with crosslinking. Suitable reactive materials are, for example, heat-curable binders, such as urea-formaldehyde adducts, one- or two-component systems based on epoxy resins, polyacrylates and polymethacrylates. In this process, too, the entire top or bottom of the product is treated with at least one reactive material.

It is the object of the invention to improve the properties of paper and paper products, in particular the stiffness, printability, laminatability and biocidal action with respect to microorganisms, in such a way that an adequate effect is achieved in comparison with known processes even with a smaller amount of finishing agents.

The object is achieved, according to the invention, by a process for finishing paper and paper products by treating the surface of paper or paper products with at least one finishing agent, if at least one finishing agent is applied in the form of a pattern on the top and/or bottom of paper or paper products. The finishing agent is preferably applied with the aid of a printing process on the top and/or bottom of paper or paper products. Such printing processes are part of the prior art. They are usually used for printing on sized or coated papers or on textiles with print pastes which differ from finishing agents for paper. The finishing agent can be printed, for example, by the screen printing, inkjet printing, flexographic printing or offset printing process on the top and/or the bottom of paper or paper products.

Preferably, the finishing agent is printed by the inkjet printing process on the top of paper or paper products. The paper may be, for example, unsized or may be an engine-sized paper or paper product. Suitable engine sizes are, for example, alkyldiketenes, alkenylsuccinic anhydrides or rosin size.

The invention also relates to papers and paper products which in each case are obtainable by the process according to the invention. These are substantially writing and printing papers, packaging papers, corrugated board, wallpapers, cardboard, filters and laminated materials, for example comprising a composite of board or paper and at least one film of a thermoplastic, for example polyethylene, polypropylene, polyamide, polyester or polycarbonate.

The finishing agents are printed, for example, in the form of a grid or of a rhombus or in spiral, circular, two-dimensional, strip or dot form on the top and/or bottom of the paper or paper products, it being possible for a pattern to be arranged in ordered or in random form (stochastically). The finishing agents are always applied according to the pattern. In contrast to known methods for applying finishing agents to paper, in which the finishing agent is applied over the whole top or bottom of paper, the finishing agent in the process according to the invention is applied to the surface of the paper in a manner such that the whole area is not coated therewith. For example, the proportion with the area printed altogether with finishing agent is from 0.1 to 90, preferably from 1 to 70, % and is in general in the range from 10 to 50%. The other part of the surface of the paper which is not treated with a finishing agent remains untreated. After the printing, the printed paper or paper product is dried and, if appropriate, heated to a temperature at which the finishing agents crosslink, for example to temperatures in the range from 35 to 200° C.

The effect achieved in each case with the aid of the process according to the invention, for example the stiffness of a paper, is dependent on a plurality of factors, especially on the composition and amount of the finishing agent, on the structure of the finishing agent printed in each case on the paper and on the orientation of the paper, i.e. the stiffness of the paper depends on the orientation of the cellulose fibers. In the case of a paper sheet, it differs in the machine direction compared with the direction transverse thereto. The finishing agent is applied in the form of a pattern and can be printed, for example, in the form of a grid, of a rhombus or of a polygon (e.g. hexagon, octagon) or in spiral, circular, two-dimensional, strip or dot form on the top and/or bottom of the paper or paper products. The individual strips of a grid or of a rhombus may have different dimensions, for example a thickness of from 0.1 to 100 mm, preferably from 1 to 10 mm, and a length of from 0.1 to 100 mm, preferably from 1 to 10 mm. The distance between the individual strips of a grid, i.e. the unprinted areas may have, for example, a spacing of from 0.1 to 100 nm, preferably from 1 to 10 mm. The grid may be square, rectangular or rhombic. If the paper is printed with strips, the strips can extend over the total length or width of the paper.

The paper may also be printed in a dot-like manner with a multiplicity of dots or in a two-dimensional manner, two-dimensional being understood as meaning that a larger area is provided with a finishing agent, for example an area having the dimensions 2×2 to 10 cm or 4×1 to 10 cm. Circular areas which are printed on a paper may have, for example, a diameter of from 1 mm to 10 cm.

The process according to the invention can be integrated into the papermaking process. Thus, it is possible, for example, to print a finishing agent onto the still moist paper and then to dry the paper thus treated and, if appropriate, to heat it to a higher temperature (from 170 to 200° C.) in order to crosslink the finishing agent printed on. However, it is also possible to print a finishing agent onto the paper during the drying process or thereafter, to dry the printed material and, if appropriate, to crosslink it. At least one finishing agent can be printed on the paper products in a corresponding manner during or after the production.

Suitable papers which are finished according to the invention are preferably all paper types, in particular base papers. Paper products are to be understood as meaning, for example, packaging papers, corrugated board, wallpapers, cardboard and laminated materials, for example comprising a composite of board or paper and at least one film of a thermoplastic. For example, for the production of the papers and of the paper products, it is possible to start from cellulose fibers of all types, both from natural and from recovered fibers, in particular from fibers from wastepaper, which are generally used as a mixture with virgin fibers. Virgin fibers are to be understood as meaning cellulose fibers which have not yet been processed to a paper product or which have not yet been dried. Suitable fibers for the production of the pulps are all qualities customary for this purpose, for example mechanical pulp, bleached and unbleached chemical pulp and paper stocks from all annual plants. Mechanical pulp includes, for example, groundwood, thermomechanical pulp (TMP), chemothermomechanical (CTMP), pressure groundwood, semi-chemical pulp, high-yield pulp and refiner mechanical pulp (RMP). For example, sulfate, sulfite and soda pulps are suitable as chemical pulp. Unbleached pulp, which is also referred to as unbleached kraft pulp, is preferably used. Suitable annual plants for the production of paper stocks are, for example, rice, wheat, sugar cane and kenaf.

According to the invention, the paper or the paper products is or are printed with a finishing agent according to a pattern. The finishing agent used is, for example, a strength agent, a water repellant, a hydrophilizing agent, a paper coating slip or an indicator system for biomaterials (for example for bacteria or viruses). At least one agent which increases the stiffness of paper is particularly preferably used for finishing. These agents generally also simultaneously increase the dry and/or wet strength of paper and paper products. Further finishing agents are customary dry strength agents and/or wet strength agents for paper.

According to the invention, in order to increase the stiffness of paper and paper products, a heat-curable binder from the group consisting of the urea-formaldehyde adducts, urea-glyoxal adducts, melamine-formaldehyde adducts, phenol-formaldehyde adducts, one- and two-component systems based on epoxy resins, polyurethanes or isocyanates, polyacrylates, polymethacrylates, styrene/(meth)acrylate copolymer dispersions and/or styrene/butadiene/(meth)acrylic acid copolymer dispersions is preferably used. In some cases, the use of mixtures of at least two reactor materials is of interest, for example mixtures of melamine/urea-formaldehyde condensates. The reactive materials may be present as aqueous solution or as aqueous dispersion. Here, transitions between solution and dispersion are possible. If dispersions are used, for example, the mean particle diameter of the polymer particles dispersed in water is below 1 μm, preferably below 500 nm and in general in the range from 10 to 100 nm.

The aqueous solution and/or dispersion thus comprises, for example, a group of a reactive, crosslinkable material which may consist of

-   (i) at least one reactive substance which forms a polymer, -   (ii) if appropriate, at least one C₁₋₅-alcohol, at least one polyol     or mixtures thereof and -   (iii) at least one catalyst.

Examples of (i) a reactive substances which forms a polymer are urea-glyoxal adducts and derivatives thereof, e.g. 1,3-bis(hydroxymethyl)-4,5-dihydroxyimidazolidin-2-one (referred to as “DMDHEU” below). When printing on paper or paper products, it can be used either alone or together with (ii) at least one C₁₋₅-alcohol, one polyol or mixtures thereof. If 1,3-bis(hydroxymethyl)-4,5-dihydroxyimidazolidin-2-one is used together with an alcohol and/or a polyol as a finishing agent, modified 1,3-bis(hydroxymethyl)-4,5-dihydroxyimidazolidin-2-ones (referred to as “mDMDHEU” below) accordingly forms. Such compounds are disclosed, for example, in U.S. Pat. No. 4,396,391 and WO 98/29393. These are reaction products of 1,3-bis(hydroxymethyl)-4,5-dihydroxyimidazolidin-2-one with at least one C₁₋₅-alcohol, at least one polyol or mixtures thereof.

The compounds of the group (ii) include C₁₋₅-alcohols, for example methanol, ethanol, n-propanol, isopropanol, n-butanol, isobutanol, tert-butanol and n-pentanol, methanol being preferred, and polyols, such as ethylene glycol, diethylene glycol, 1,2- and 1,3-propylene glycol, 1,2-, 1,3-, and 1,4-butylene glycol, glycerol, trimethylolpropane and polyalkylene glycols, such as polyethylene glycol, polypropylene glycol and block copolymers of ethylene glycol and propylene glycol. Polyethylene glycols of the formula HO(CH₂CH₂O)_(n)H where n is from 3 to 20 and diethylene glycol are preferred.

In order to prepare modified 1,3-bis(hydroxymethyl)-4,5-dihydroxyimidazolidin-2-one (DMDHEU), DMDHEU and the monohydric alcohol and/or the polyol are mixed, the monohydric alcohol and/or the polyol being used in an amount of from 0.1 to 2.0 mol equivalents each, based on DMDHEU. The mixture of DMDHEU, monohydric alcohol and/or polyol is reacted, for example, at temperatures of from 20 to 70° C. and a pH of from 1 to 2.5, the pH being adjusted to 4 to 8 after reaction.

(i) a reactive substance which forms a polymer is to be understood as meaning both urea-formaldehyde adducts and urea-glyoxal adducts and derivatives of each of them. The following compounds may be mentioned by way of example: dimethylolurea, bis(methoxymethyl)urea, tetramethylolacetylenediurea, methylolmethylurea and 1,3-dimethyl-4,5-dihydroxyimidazolidin-2-one, 1,3-bis(hydroxymethyl)imidazolidin-2-one or mixtures thereof. These compounds of the group (i) can, if appropriate, also be used as finishing agents in the presence of (ii) at least one C₁₋₅-alcohol, at least one polyol or mixtures thereof. Suitable alcohols and polyols have already been mentioned above. Methanol, diethylene glycol or mixtures thereof are preferred.

The aqueous solution of the finishing agent comprises the reactive compounds of the group (i) and the compounds of the group (ii), for example, in a concentration of from 1 to 70% by weight, preferably from 10 to 60% by weight and in particular from 20 to 60% by weight. The impregnating agent preferably comprises 1,3-bis(hydroxymethyl)-4,5-dihydroxyimidazolidin-2-one (DMDHEU) as a compound of the group (i).

In addition to (i) and, if appropriate, (ii), the finishing agent always comprises a catalyst (iii). Suitable catalysts (iii) are, for example, metal salts from the group consisting of metal halides, metal sulfates, metal nitrates, metal tetrafluoroborates, metal phosphates or mixtures thereof. Individual examples of (iii) are magnesium chloride, magnesium sulfate, zinc chloride, lithium chloride, lithium bromide, boron trifluoride, aluminum chloride, aluminum sulfate, zinc nitrate and sodium tetrafluoroborate. Said compounds can be used either alone or in a mixture as the catalyst.

Further suitable compounds (iii) are ammonium salts, such as ammonium chloride, ammonium sulfate, ammonium oxalate, diammonium phosphate or mixtures thereof. In addition, organic and/or inorganic acids can be used as the catalyst. Examples of these are maleic acid, formic acid, acetic acid, priopionic acid, citric acid, tartaric acid, oxalic acid, p-toluenesulfonic acid, hydrochloric acid, sulfuric acid, boric acid or mixtures thereof.

Magnesium chloride, zinc chloride, magnesium sulfate, aluminum sulfate or mixtures of these compounds are preferably used as compounds of the group (iii). Magnesium chloride is particularly preferred.

The catalyst (iii) is present, for example in a concentration of from 0.1 to 10% by weight, preferably from 0.2 to 8% by weight, particularly preferably from 0.3 to 5% by weight, based on the components (i)-(iii) of the reactive material.

Among the above-described products which comprise formaldehyde incorporated in the form of condensed units, in particular low-formaldehyde condensates are used. In the present context, low-formaldehyde is to be understood as meaning that the reactive materials comprise no substantial amounts of free formaldehyde and that no substantial amounts of formaldehyde are released even on drying or curing of the cellulose fibers or paper products treated therewith. In general, such reactive materials comprise <100 ppm of formaldehyde.

Further reactive materials which react with themselves and/or cellulose fibers with crosslinking are formaldehyde-free, heat-curable binders. Such binders are described, for example, in the following publications, which are hereby incorporated by reference in the disclosure of the present invention, namely U.S. Pat. No. 4,076,917, EP-A 0 445 578, EP-A 0 583 086, EP-A 0 651 088, WO 97/31036, page 4, line 12 to page 12, line 14, WO 97/31059, page 2, line 22 to page 12, line 5, WO 97/31060, page 3, line 8 to page 12, line 36, DE-A 199 49 591, page 3, line 5 to page 7, line 38, WO 01/27163, page 5, line 34 to page 22, line 2 and the radiation-curable binders disclosed in DE-A 199 17 965.

Suitable heat-curable binders apart from the binders which are described in the abovementioned publications are all curable binders which are described in the literature, for example, for strengthening fiber webs and/or which are used for this purpose in practice, such as heat-curable resins based on phenol and formaldehyde, the abovementioned melamine-formaldehyde and urea-formaldehyde resins, urea-glyoxal resins and in particular formaldehyde-free one- and two-component systems based on epoxy resins or polyurethanes, polyacrylates, polymethacrylates, polyvinyl acetates, styrene/acrylate copolymer dispersions, styrene/methacrylate copolymer dispersions, styrene/butadiene/(meth)acrylic acid copolymer dispersions and mixtures of said dispersions with a mixture of a polycarboxylic acid and a polyhydric alcohol as a crosslinking component.

Examples of preferred finishing agents are heat-curable binders in the form of mixtures of

-   (a) a polymer which is obtainable by free radical polymerization and     which comprises from 5 to 100% by weight of an ethylenically     unsaturated carboxylic anhydride or of an ethylenically unsaturated     dicarboxylic acid whose carboxyl groups can form anhydride groups,     incorporated in the form of polymerized units, and -   (b) at least one alkanolamine which comprises at least two hydroxyl     groups in the molecule and/or at least one polyhydric alcohol.

Specific examples of such mixtures are aqueous solutions and/or dispersions of a copolymer of 80% by weight of acrylic acid and 20% by weight of maleic acid, having a molar mass M_(w) of from 15 000 to 900 000, which solutions and/or dispersions comprise from about 40 to 60% by weight of solids, in combination with triethanolamine or aqueous solutions of a copolymer of 55% by weight of acrylic acid and 45% by weight of the maleic acid in combination with triethanolamine. These binders can, if appropriate, comprise an esterification catalyst and/or a compound comprising bound phosphorus, such as hypophosphorous acid, as a reaction accelerator.

The copolymer (a) described above may also be composed, for example, of

-   -   from 50 to 99.5% by weight of at least one ethylenically         unsaturated mono- or dicarboxylic acid,     -   from 0.5 to 50% by weight of at least one ethylenically         unsaturated compound from the group consisting of the esters of         ethylenically unsaturated monocarboxylic acids and the         monoesters and the diesters of ethylenically unsaturated         dicarboxylic acids with an amine having at least one hydroxyl         group and     -   up to 20% by weight of another monomer.

Heat-curable, aqueous compositions which comprise at least one copolymer (a) and at least one alkanolamine or higher-functional β-hydroxyalkylamine and/or at least one polyhydric alcohol can, if appropriate, additionally comprise at least one surfactant.

Further heat-curable binders which can be used as finishing agents are based on aqueous mixtures of

-   -   polycarboxylic acids, such as polyacrylic acid, polymethacrylic         acid, copolymers of acrylic acid and maleic acid, copolymers of         methacrylic acid and maleic acid, copolymers of ethylene and         maleic acid, styrene and maleic acid, or copolymers of acrylic         acid or methacrylic acid and esters of acrylic or methacrylic         acid with, preferably, monohydric alcohols comprising 1 to 24         carbon atoms, the polycarboxylic acids having a K value of from         50 to 100 (measured in unneutralized form of the polycarboxylic         acids according to H. Fikentscher in dimethylformamide at 25° C.         and a polymer concentration of 0.1% by weight) and     -   polyhydric alcohols, such as trimethylpropane, glycerol,         2-hydroxymethylbutane-1,4-diol or polyvinyl alcohol, and/or         polyfunctional amines and/or alkanolamines.

Polycarboxylic acids, polyhydric alcohols, alkanolamines and polyfunctional amines are preferably used in amounts such that the number of acid functions is equivalent to the total number of alcoholic hydroxyl and amine functions, cf. EP-A 0 445 578. In addition, crosslinkable materials which consist of an aqueous solution of a polycarboxylic acid (homo- or copolymer), preferably having a molar mass M_(w) of 10 000 or less, and a polyol, such as triethanolamine, and in which the ratio of the equivalents of hydroxyl groups to equivalents of carboxyl groups is in the range from 0.4:1 to 1.0:1 are suitable, cf. EP-A 0 990 727.

In the process according to the invention, reactive materials which are sold under the trade name Acrodur® by BASF Aktiengesellschaft are particularly advantageously used as finishing agents. An example of this is an aqueous styrene/acrylate polymer dispersion which is modified with a polycarboxylic acid and a polyhydric alcohol as crosslinking component. It crosslinks at a temperature of only 130° C. However, in order to achieve high production rates, the crosslinking is preferably carried out at temperatures of from 180 to 200° C. A further formaldehyde-free binder is commercially available, for example, as a colorless to slightly yellowish, clear, aqueous solution of a modified polycarboxylic acid with a polyhydric alcohol as crosslinking component. It crosslinks, for example, at drying temperatures of from about 160 to 180° C.

Formaldehyde-free reactive materials which comprise at least one polycarboxylic acid and at least one polyhydric alcohol and/or alkanolamine or polyfunctional amine are particularly preferred. Compositions which comprise these reactive agents can, if appropriate, also comprise further formaldehyde-free polymers, e.g. polyacrylates, which are sold under the trade name Acronal® by BASF Aktiengesellschaft. The aqueous solutions and/or dispersions of a reactive material which are used for printing comprise the reactive material, for example, in an amount of from 1 to 70% by weight, preferably from 10 to 60% by weight and in general from 30 to 50% by weight.

Further finishing agents are water repellants from the group consisting of alkyldiketenes, alkenylsuccinic anhydrides, rosin size, polymer sizes based on styrene/(meth)acrylate polymers and isocyanates. Preferred alkyldiketenes are C₁₄- to C₂₂-alkyl- or alkenyldiketenes. They are prepared, for example, from the corresponding acyl chlorides by elimination of hydrogen chloride with tertiary amines. The diketenes which can be used according to the invention may carry saturated or unsaturated, branched or cyclic hydrocarbon radicals. Examples of such alkyldiketenes are tetradecyldiketene, hexadecyldiketene, octadecyldiketene, docosyldiketene, palmityldiketene, oleyldiketene, stearyldiketene and behenyldiketene. Stearyldiketene, palmityldiketene, oleyldiketene, behenyldiketene, isostearyidiketene or mixtures of alkyl diketenes, e.g. mixtures of behenyldiketene and stearyldiketene or mixtures of stearyldiketene and palmityldiketene, are preferably used.

Alkenylsuccinic anhydrides are described in detail, for example, in U.S. Pat. No. 3,102,064, EP-A 0 609 879 and EP-A-0 593 075. All alkenylsuccinic anhydrides which have been described to date in the literature as engine sizes for paper are also suitable according to the invention as finishing agents, either alone, or in combination with alkyldiketenes. Suitable alkylsuccinic anhydrides comprise, in the alkyl group, an alkyl radical having at least 6 carbon atoms, preferably a C₁₄- to C₂₄-olefin radical. Particularly preferred alkenylsuccinic anhydrides comprise 16 to 22, in general 16 to 18, carbon atoms in the alkenyl group. They may comprise linear, additionally unsaturated or branched alkenyl groups. Alkenylsuccinic anhydrides are obtainable, for example, from α-olefins, which are first isomerized. This gives a mixture of different isomers, which is then reacted with maleic anhydride in an ene reaction to give succinic anhydrides. Alkenylsuccinic anhydrides are prepared according to EP-A 0 593 075 by reaction of propylene oligomers or n-butylene oligomers with maleic anhydride. Examples of this group of reactive sizes are decenylsuccinic anhydride, dodecenylsuccinic anhydride, octenylsuccinic anhydride and n-hexadecenylsuccinic anhydride. The individual isomeric succinic anhydride may have a different sizing effect. Thus, for example, 2- and 3-hexadecenyl succinic anhydrides are not as effective engine sizes as the isomeric 4-, 5-, 6-, 7- and 8-hexadecenylsuccinic anhydrides.

A further finishing agent in the context of the present invention is rosin size and derivatives derived therefrom, such as, for example, reaction products of rosin size and maleic anhydride. The derivatives may be branched or unsaturated, e.g. abietic acid. Moreover, polymer sizes based on styrene and (meth)acrylates, which are preferably obtainable by polymerization of the monomers in the presence of degraded starch, are suitable as finishing agents. Such sizes are disclosed, for example, in EP-A 0 276 770, EP-A 0 257 412, EP-A 0 307 812 and WO 02/14393. If sizes for paper are used according to the invention as finishing agents, sized papers which are particularly suitable as writing and printing papers are obtained.

Further finishing agents are hydrophilizing agents and water repellants, such as ethylene copolymer waxes, polymers comprising siloxane groups and/or polymers comprising bound fluorine, such as Lodyne® from Clariant, and paper coating slips (aqueous mixtures of at least one pigment and at least one binder, based in each case on an acid group-comprising copolymer of styrene and butadiene or of styrene and (meth)acrylate) and biocides. The papers and paper products finished with a biocide are used, for example, for applications in the sanitary or hygiene area, in the food sector, in particular for the packaging of foods, or for industrial applications, e.g. for filters.

Particularly suitable biocides are compounds from the group consisting of polymers comprising vinylamine units, polymers comprising ethylenimine units, combinations of at least one polymer comprising vinylamine units and at least one organic quaternary ammonium salt and combinations of at least one monomer comprising ethylenimine units and at least one organic quaternary ammonium salt. The suitable polymers and the organic quaternary ammonium salts are known. Furthermore, DE-A 196 08 555 discloses use of polymers comprising vinylamine units or ethylenimine units as biocidal active substances, for example as slime control agents in papermaking. The polymers which are described in DE-A 196 08 555 and comprise vinylamine units or ethylenimine units are applied, preferably printed on, by the process according to the invention as a biocide on paper or paper products in the form of a pattern. Regarding the details of the polymers suitable according to the invention, reference is therefore made to the abovementioned DE-A 196 08 555, page 1, line 43 to page 10, line 8.

Polymers comprising vinylamine units are obtainable by a two-stage process by polymerization of N-vinylcarboxamides and hydrolysis of the resulting poly(N-vinylcarboxamides) with formation of vinylamine units, cf. U.S. Pat. No. 4,421,602, U.S. Pat. No. 5,334,287, EP-A 0 216 387, U.S. Pat. No. 5,981,689, WO 00/63295, U.S. Pat. No. 6,121,409 and U.S. Pat. No. 6,132,558. Examples of N-vinylcarboxamides are N-vinylformamide, N-vinyl-N-methylformamide, N-vinylacetamide, N-vinyl-N-methylacetamide, N-vinyl-N-ethylacetamide and N-vinylpropionamide. Said monomers can be polymerized either alone, as a mixture with one another or together with other monomers. N-vinylformamide is preferred.

Suitable monoethylenically unsaturated monomers which are copolymerized with the N-vinylcarboxamide are all compounds copolymerizable therewith. Examples of these are vinyl esters of saturated carboxylic acids of 1 to 6 carbon atoms, such as vinyl formate, vinyl acetate, N-vinylpyrrolidone, vinyl propionate and vinyl butyrate, and vinyl ethers, such as C₁- to C₆-alkyl vinyl ethers, e.g. methyl or ethyl vinyl ether. Further suitable comonomers are esters of alcohols having, for example, 1 to 6 carbon atoms, amides and nitriles of ethylenically unsaturated C₃- to C₆-carboxylic acids, for example methyl acrylate, methyl methacrylate, ethyl acrylate, ethyl methacrylate and dimethyl maleate, acrylamide and methacrylamide and acrylonitrile and methacrylonitrile.

Further suitable compounds copolymerizable with N-vinylcarboxamides are carboxylic esters of glycols or polyalkylene glycols, in each case only one OH group being esterified, e.g. hydroxyethyl acrylate, hydroxyethyl methacrylate, hydroxypropyl acrylate, hydroxybutyl acrylate, hydroxypropyl methacrylate, hydroxybutyl methacrylate and monoesters of acrylic acid with polyalkylene glycols having a molar mass of from 500 to 10 000. Further suitable comonomers are esters of ethylenically unsaturated carboxylic acids with aminoalcohols, such as, for example, dimethylaminoethyl acrylate, dimethylaminoethyl methacrylate, dimethylaminoethyl acrylate, dimethylaminoethyl methacrylate, dimethylaminopropyl acrylate, dimethylaminopropyl methacrylate, diethylaminopropyl acrylate, dimethylaminobutyl acrylate and diethylaminobutyl acrylate. The basic acrylates can be used in the form of the free bases, of the salts with mineral acids, such as hydrochloric acid, sulfuric acid or nitric acid, of the salts with organic acids, such as formic acid, acetic acid or propionic acid, or of the sulfonic acids or in quaternized form. Suitable quaternizing agents are, for example, dimethyl sulfate, diethyl sulfate, methyl chloride, ethyl chloride or benzyl chloride. Further suitable comonomers are amides of ethylenically unsaturated carboxylic acids, such as acrylamide, methacrylamide and N-alkylmono- and diamides of monoethylenically unsaturated carboxylic acids having alkyl radicals of 1 to 6 carbon atoms, e.g. N-methylacrylamide, N,N-dimethylacrylamide, N-methylmethacrylamide, N-ethylacrylamide, N-propylacrylamide and tert-butylacrylamide, and basic (meth)acrylamides, such as, for example, dimethylaminoethylacrylamide, dimethylaminoethylmethacrylamide, diethylaminoethylacrylamide, diethylaminoethylmethacrylamide, dimethylaminopropylacrylamide, diethylaminopropylacrylamide, dimethylaminopropylmethacrylamide and diethylaminopropylmethacrylamide.

Furthermore, N-vinylpyrrolidone, N-vinylcaprolactam, acrylonitrile, methacrylonitrile, N-vinylimidazole and substituted N-vinylimidazoles, such as, for example, N-vinyl-2-methylimidazole, N-vinyl-4-methylimidazole, N-vinyl-5-methylimidazole and N-vinyl-2-ethylimidazole, and N-vinylimidazolines, such as N-vinylimidazoline, N-vinyl-2-methylimidazoline and N-vinyl-2-ethylimidazoline, are suitable as comonomers. N-vinylimidazoles and N-vinylimidazolines are used not only in the form of free bases but also in the form neutralized with mineral acids or organic acids or in quaternized form, the quaternization preferably being carried out with the dimethyl sulfate, diethyl sulfate, methyl chloride or benzyl chloride. Diallydialkylammonium halides, such as, for example, diallyldimethylammonium chloride, are also suitable.

The copolymers comprise, for example,

-   -   from 95 to 5 mol %, preferably from 90 to 10 mol %, of at least         one N-vinylcarboxamide, preferably N-vinylformamide, and     -   from 5 to 95 mol %, preferably from 10 to 90 mol %, of         monoethylenically unsaturated monomers         incorporated in the form of polymerized units. The comonomers         are preferably free of acid groups.

The polymerization of the monomers is usually carried out in the presence of free radical polymerization initiators. The homo- and copolymers can be obtained by known processes; for example they are obtained by solution polymerization in water, alcohols, ethers or dimethylformamide or in mixtures of different solvents, by precipitation polymerization, inverse suspension polymerization (polymerization of an emulsion of a monomer-containing aqueous phase in an oil phase) and polymerization in a water-in-water emulsion, for example in which an aqueous monomer solution is dissolved or emulsified in an aqueous phase and polymerization for formation of an aqueous dispersion of a water-soluble polymer, as described, for example, in WO 00/27893. After the polymerization, the homo- and copolymers which comprise N-vinylcarboxamide units incorporated in the form of polymerized units are partly or completely hydrolyzed as described below.

In order to prepare polymers comprising vinylamine units, it is preferable to start from homopolymers of N-vinylformamide or from copolymers which are obtainable by copolymerization of

-   -   N-vinylformamide with     -   vinyl formate, vinyl acetate, vinyl propionate, acrylonitrile,         methyl acrylate, ethyl acrylate and/or methyl methacrylate         and subsequent hydrolysis of the homo- or copolymers with         formation of vinylamine units from the N-vinylformamide units         incorporated in the form of polymerized units, the degree of         hydrolysis being, for example, from 1 to 100 mol %, preferably         from 25 to 100 mol %, particularly preferably from 50 to 100 mol         % and especially preferably from 70 to 100 mol %. The degree of         hydrolysis corresponds to the content of vinylamine groups in         the polymers, in mol %. The hydrolysis of polymers described         above is effected by known methods, by the action of acids (e.g.         mineral acids, such as sulfuric acid, hydrochloric acid or         phosphoric acid, carboxylic acids, such as formic acid or acetic         acid, or sulfonic acids or phosphonic acids), bases or enzymes,         as described, for example, in DE-A 31 28 478 and U.S. Pat. No.         6,132,558. When acids are used as hydrolysis agents, the         vinylamine units of the polymers are present as the ammonium         salts, whereas the free amino groups are formed in the case of         hydrolysis with bases.

In most cases, the degree of hydrolysis of homo- and copolymers used is from 85 to 95 mol %. The degree of hydrolysis of the homopolymers is equivalent to the content of vinylamine units in the polymers. In the case of copolymers which comprise vinyl esters incorporated in the form of polymerized units, hydrolysis of the ester groups with formation of vinyl alcohol units can occur in addition to the hydrolysis of the N-vinylformamide units. This is the case in particular when the hydrolysis of the copolymers is carried out in the presence of sodium hydroxide solution. Acrylonitrile incorporated in the form of polymerized units is likewise chemically modified in the hydrolysis. Here, for example, amido groups or carboxyl groups form. The homo- and copolymers comprising vinylamine units can, if appropriate, comprise up to 20 mol % of amidine units, which form, for example, by reaction of formic acid with two neighboring amino groups or by intramolecular reaction of an amino group with a neighboring amido group, e.g. of N-vinylformamide incorporated in the form of polymerized units.

The average molar mass M_(w) of the polymers comprising vinylamine units are, for example, from 500 to 10 million, preferably from 750 to 5 million and particularly preferably from 1 000 to 2 million g/mol (determined by light scattering). This molar mass range corresponds, for example, to K values of from 30 to 250, preferably from 60 to 100 (determined according to H. Fikentscher in 5% strength aqueous sodium chloride solution at 25° C., a pH of 7 and a polymer concentration of 0.5% by weight). Polymers which comprise vinylamine units and have K values of from 85 to 95 are particularly preferably used as a biocide.

The polymers comprising vinylamine units have, for example, a charge density (determined at pH 7) of from 0 to 18 meq/g, preferably from 5 to 18 meq/g and in particular from 10 to 16 meq/g.

The polymers comprising vinylamine units are preferably used in salt-free form. Salt-free aqueous solutions of polymers comprising vinylamine units can be prepared, for example, from the salt-containing polymer solutions described above with the aid of ultrafiltration or with suitable membranes at cut-offs of, for example, from 1000 to 500 000 dalton, preferably from 10 000 to 300 000 dalton.

Derivatives of polymers comprising vinylamine units may also be used. Thus, it is possible, for example, to prepare a multiplicity of suitable derivatives from the polymers comprising vinylamine units for amidation, alkylation, sulfonamide formation, urea formation, thiourea formation, carbamate formation, acylation, carboxymethylation, phosphonomethylation or Michael addition of the amino groups of the polymer. Of particular interest here are uncrosslinked polyvinylguanidines, which are obtainable by reaction of polymers comprising vinylamine units, preferably polyvinylamines, with cyanamide (R¹R²N—CN, where R¹, R² are H, C₁- to C₄-alkyl, C₃- to C₆-cycloalkyl, phenyl, benzyl, alkyl-substituted phenyl or naphthyl), cf. U.S. Pat. No. 6,087,448, column 3, line 64 to column 5, line 14.

The polymers comprising vinylamine units also comprise hydrolyzed graft polymers of, for example, N-vinylformamide on polyalkylene glycols, polyvinyl acetate, polyvinyl alcohol, polyvinylformamides, polysaccharides, such as starch, oligosaccharides or monosaccharides. The graft polymers are obtainable by, for example, subjecting N-vinylformamide to free radical polymerization in an aqueous medium in the presence of at least one of said grafting bases, if appropriate together with copolymerizable other monomers, and subsequently hydrolyzing the grafted-on vinylformamide units in a known manner to give vinylamine units.

Preferred polymers comprising vinylamine units are hydrolyzed homopolymers of N-vinylformamide having a degree of hydrolysis of from 1 to 100 mol %, preferably from 25 to 100 mol %, and copolymers of N-vinylformamide and vinyl formate, vinyl acetate, vinyl propionate, acrylonitrile, methyl acrylate, ethyl acrylate and/or methyl methacrylate, having a degree of hydrolysis of from 1 to 100 mol %, preferably from 25 to 100 mol %, and K values of 30 to 150, in particular from 60 to 100. The abovementioned partly or completely hydrolyzed homopolymers of N-vinylformamide are particularly preferably used in the process according to the invention.

Typical members of these homopolymers of N-vinylformamide are known under the trade names Catiofast® VFH, Catiofast® VSH and Catiofast® VMP from BASF Aktiengesellschaft.

The polyvinylamine preferably comprises from 0.1 to 22 milliequivalents (meq), particularly preferably from 5 to 18 meq, of cationic groups per gram of polyvinylamine. The polymers comprising vinylamine units are used, for example, in the form of an aqueous dispersion or solution.

The polymers comprising ethylenimine unites are preferably polyethylenimines which are obtainable by polymerization of ethylenimine in the presence of, as a catalyst, acids, Lewis acids or compounds eliminating acids. Such catalysts are, for example, alkyl halides, such as methyl chloride, ethyl chloride, propyl chloride, methylene chloride, trichloromethane, carbon tetrachloride or tetrabromomethane. The polyethylenimines have, for example, molar masses M_(w) in the range from 120 to 10 million, preferably from 500 to 500 000 and in particular from 1000 to 50 000. Polymers which are obtainable by grafting polyamidoamines with ethylenimine or by grafting polymers of open-chain N-vinylcarboxamides with ethylenimine are also suitable as compounds comprising ethylenimine units. Grafted polyamidoamindes are disclosed, for example, in U.S. Pat. No. 4,144,123. The polymers comprising ethylenimine units have, for example, a charge density (measured at pH 7) of from 0.1 to 22 meq (milliequivalents), preferably from 4 to 10 meq. They are preferably used in aqueous solution.

The above-described polymers comprising vinylamine or ethylenimine units are used either alone or in combination with an organic, quaternary ammonium salt as a biocide. Such ammonium salts preferably comprise at least one hydrophobic molecular group, preferably one to four, particularly preferably one to three, very particularly preferably two or three and in particular three hydrophobic molecular groups, bonded to the N atoms, such as, in particular, C₁- to C₃₀-alkyl groups.

Particularly effective biocides of ammonium salts preferably have at least one reactive group which results in or promotes binding of the ammonium salt to the substrate surface. The reactive group may be an organic molecular group which comprises at least one functional group which can react with the substrate surface, such as, in particular, epoxy groups, hydroxyl groups, acid groups and alkoxy groups. The ammonium salts preferably comprises, as the reactive group, an alkoxylated silane which is bound by a spacer to the N atom. Such ammonium salts are disclosed, for example, in WO 2004/087226, in particular in claim 6.

The quaternary ammonium salt is preferably a low molecular weight compound and has in particular a molecular weight of less than 2000 g/mol, particularly preferably less than 1500 g/mol, in particular from 200 to 1000 g/mol. It is used in particular in the form of an aqueous dispersion or preferably of an aqueous solution. Like the polymers comprising amino groups, the organic, quaternary polymer, too, can be applied alone as a biocide according to a pattern to the surface of paper or paper products. Preferably, however, it is used in combination with at least one polymer comprising vinylamine units and/or at least one polymer comprising ethylenimine units. It is easiest to start from commercially available aqueous solutions or dispersions of the polymers comprising amino groups, to mix them with an aqueous solution of the quaternary amine and then to print the mixture thus obtainable on a paper. However, it is also possible first to print according to a pattern on a paper or a paper product separately with a polymer comprising vinylamine units and/or a polymer comprising ethylenimine units and then—if appropriate after a drying step—to print on at least one organic, quaternary amine, likewise in the form of a pattern, and then to dry the printing material. As a result, a mixture of the two biocides is then present on the substrate surface in this case too.

Independently of the form of use, the proportion of the vinylamine and/or polyethylenimine is from 1 to 99% by weight, preferably from 10 to 90% by weight and particularly preferably from 30 to 70% by weight, based on the sum of the weights of polymer and ammonium salt (solid, without solvent). Accordingly, the proportion of the ammonium salt is likewise from 1 to 99% by weight, preferably from 10 to 90% by weight and particularly preferably from 30 to 70% by weight.

A mixture of polyvinylamine and ammonium salt is preferably used; in particular, it is an aqueous solution which comprises the two constituents. It preferably comprises from 0.01 to 5% by weight of biocide (sum of polymer and ammonium salt). Treatment of the paper or of the paper product over the whole area with the solution or dispersion, i.e. preferably printing of the biocide according to a pattern on the substrate, can be effected at room temperature or directly after sheet formation in the papermaking process before, during or after drying. After the drying, the paper or paper product is appropriately finished.

The amount of biocide (sum of polymer and ammonium salt) is preferably from 0.001 to 1000 mg, particularly preferably from 0.1 to 10 mg, per square meter of surface of the substrate to be finished with the biocide.

The substrates finished with the biocide may be, for example, products for medical applications, applications in the sanitary or hygiene area, in the food area, in particular in food packaging, or substrates for a wide range of industrial applications, in particular filters, for example for air-conditioning systems.

Compared with the known impregnation processes, the process according to the invention has the advantage that substantially smaller amounts of finishing agent are required for approximately comparable properties of the papers and paper products and hence papers and paper products can be more economically produced.

Unless otherwise evident from the context, the stated percentages in examples are percent by weight.

EXAMPLE Determination of the Stiffness

A DIN A4 sheet was printed according to the invention with a finishing agent, dried, and conditioned for 24 hours at 25° C. and 60% relative humidity. The measurements were carried out at room temperature under the respective prevailing air pressure. A test piece having the dimensions 100×100 mm was cut from the center of the DIN A4 sheet printed according to the invention with the finishing agent. The test piece was then fixed between two blocks of wood so that 50% of the test piece projected. That part of the test piece which projected from the block was then loaded with weights of from 1 to 50 g by placing the weights in the middle of the test piece at a distance of 10 mm from the outer edge. As soon as the end of the test piece projecting from the block had reached 25 mm or the weight had fallen from the paper, the load required for this purpose in g was measured as a measure of the stiffness.

The following finishing agents were used:

-   Finishing agent 1: Mixture of a polycarboxylic acid and a     polyfunctional amine in the form of a 35% strength aqueous solution     (Acrodur® 950L) -   Finishing agent 2: Mixture of a polycarboxylic acid and a     polyfunctional amine in the form of a 35% strength aqueous     dispersion (Acrodur® D3515) -   Finishing agent 3: 70% strength aqueous solution of a heat-curable     urea-formaldehyde resin (Fixapret® ECO)

Examples 1 to 36 and Comparative Examples 1 to 16

DIN A4 sheets were each printed with the amounts of finishing agents stated in the table below with the aid of the inkjet printing process in the pattern likewise stated in the table. The sheets printed with the finishing agents 1 to 3 were each stored for 15 minutes at 140° C. in order to crosslink the polymers. Thereafter, the stiffness of the paper was determined in each case by the method described above. The results are shown in the table.

In the table, “Line (MD)” denotes lines which are printed on the DIN A4 sheet and which run in the machine direction of the sheet during papermaking and “Line (CD)” denotes lines which are printed on and run transverse to the machine direction.

In comparative examples 1 to 6, water was printed on the sheet in the print patterns stated in the table, and the sheet thus treated was dried in each case before the determination of the stiffness.

TABLE Stiffness Solids Amount Stiffness transverse Finishing content printed on in machine to machine agent No. [%] Printed pattern [g/m²] direction direction Example No. 1 1 12.5 Line (MD) 5 15 1 2 1 12.5 Line (CD) 5 1 20 3 1 12.5 Spiral 5 7 6 4 1 12.5 Concentric 5 7 7 circles 5 1 12.5 Square 5 10 1 6 1 12.5 Rhombus 5 20 9 7 1 25 Line (MD) 15 18 1 8 1 25 Line (CD) 20 1 16 9 1 25 Spiral 15 12 12 10 1 25 Concentric 15 12 12 circles 11 1 25 Square 20 12 1 12 1 25 Rhombus 15 22 22 13 2 12.5 Line (MD) 5 17 1 14 2 12.5 Line (CD) 5 2 23 15 2 12.5 Spiral 5 14 12 16 2 12.5 Concentric 4 17 17 circles 17 2 12.5 Square 5 25 6 18 2 12.5 Rhombus 4 7 12 19 2 25 Line (MD) 12 12 7 20 2 25 Line (CD) 15 1 24 21 2 25 Spiral 14 19 19 22 2 25 Concentric 20 21 19 circles 23 2 25 Square 14 >30 4 24 2 25 Rhombus 8 27 9 25 3 12.5 Line (MD) 4 7 1 26 3 12.5 Line (CD) 5 1 5 27 3 12.5 Spiral 4 6 7 28 3 12.5 Concentric 4 6 6 circles 29 3 12.5 Square 4 8 1 30 3 12.5 Rhombus 4 8 4 31 3 25 Line (MD) 20 16 1 32 3 25 Line (CD) 16 1 17 33 3 25 Spiral 17 12 12 34 3 25 Concentric 15 9 8 circles 35 3 25 Square 11 19 2 36 3 25 Rhombus 8 10 4 Comparative examples 1 Water Line (MD) 0 6 1 2 Water Line (CD) 0 6 1 3 Water Spiral 0 6 1 4 Water Concentric 0 4 1 circles 5 Water Square 0 5 1 6 Water Rhombus 0 5 2 7 1 Whole area 5 5 1 8 1 Whole area 20 7 2 9 1 Whole area 100 22 20 10 2 Whole area 5 4 1 11 2 Whole area 20 7 2 12 2 Whole area 100 25 23 13 3 Whole area 5 5 1 14 3 Whole area 20 6 3 15 3 Whole area 100 20 23 16 Unprinted 6 1 and uncoated test paper 

1. A process for finishing paper or a paper product comprising treating the surface of said paper or paper product with at least one finishing agent, wherein the at least one finishing agent is applied in the form of a pattern to the top and/or bottom of said paper or paper product.
 2. The process according to claim 1, wherein the finishing agent is applied with the aid of a printing process to the top and/or bottom of said paper or paper product.
 3. The process according to claim 1, wherein the finishing agent is printed on the top and/or the bottom of said paper or paper product by a screen printing, inkjet printing, flexographic printing or offset printing process.
 4. The process according to claim 1, wherein the finishing agent is printed on the top of said paper or paper product by the inkjet printing process.
 5. The process according to claim 1, wherein an engine-sized paper or paper product is used.
 6. The process according to claim 1, wherein the finishing agents are applied in the form of a grid or of a rhombus or in spiral, circular, two-dimensional, strip or dot form on the top and/or bottom of paper or paper products, the pattern printed on being present in each case in ordered or in random form.
 7. The process according to claim 1, wherein the finishing agent is a strength agent, a water repellant, a hydrophilizing agent, a paper coating slip and/or a biocide.
 8. The process according to claim 1, wherein the finishing agent is at least one agent which increases the stiffness of paper.
 9. The process according to claim 1, wherein the finishing agent is a dry strength agent and/or a wet strength agent for paper.
 10. The process according to claim 1, wherein the finishing agent is at least one water repellant selected from the group consisting of alkyldiketenes, alkylsuccinic anhydrides, rosin size, polymer sizes based on styrene/(meth)acrylate polymers, isocyanates, ethylene copolymer waxes, polymers comprising siloxane groups and polymers comprising bound fluorine.
 11. The process according to claim 1, wherein the finishing agent is at least one heat-curable binder selected from the group consisting of the urea-formaldehyde adducts, urea-glyoxal adducts, melamine-formaldehyde adducts, phenol-formaldehyde adducts, one- and two-component systems based on epoxy resins, polyurethanes or isocyanates, polyacrylates, polymethacrylates, styrene/(meth)acrylate copolymer dispersions and styrene/butadiene/(meth)acrylic acid copolymer dispersions.
 12. The process according to claim 1, wherein the finishing agent is at least one heat-curable binder comprising (a) a polymer which is obtained by free radical polymerization and which comprises from 5 to 100% by weight of an ethylenically unsaturated carboxylic anhydride or of an ethylenically unsaturated dicarboxylic acid whose carboxyl groups can form anhydride groups, incorporated in the form of polymerized units, and (b) at least one alkanolamine which comprises at least two hydroxyl groups in the molecule and/or at least one polyhydric alcohol.
 13. The process according to claim 1, wherein the finishing agent is at least one heat-curable binder comprising an aqueous mixture with at least one polycarboxylic acid and at least one polyhydric alcohol and/or at least one polyfunctional amine and/or an alkanolamine.
 14. The process according to claim 1, wherein the finishing agent is at least one biocide selected from the group consisting of polymers comprising vinylamine units, polymers comprising ethylenimine units, combinations of at least one polymer comprising vinylamine units and at least one organic quaternary ammonium salt and combinations of at least one polymer comprising ethylenimine units and at least one organic quaternary ammonium salt.
 15. A paper or paper product obtained by the process of claim
 1. 